Perform signum function on array
c = sign(a)
c = sign(a) returns an array c the
same size as a, where each element of c is
1 if the corresponding element
of a is greater than zero
0 if the corresponding element
of a is zero
-1 if the corresponding element
of a is less than zero
The elements of c are of data type int8.
sign does not support complex fi inputs.